A fuel cell is a device that converts chemical energy from a substance (e.g., referred to as a fuel) into electrical energy (e.g., electricity). Generally, the energy conversion includes a chemical reaction with oxygen or another oxidizing agent. For example, hydrogen is among a common fuel, and hydrocarbons such as natural gas and alcohols can also be used in fuel cells. For example, fuel cells differ from batteries in that they require a constant source of fuel and oxygen to operate, but can produce electricity continually provided the fuel and oxygen inputs are supplied to the fuel cell.